1. Field of the Invention
The present invention relates to a substrate mounting stage and a surface treatment method therefor, and in particular to a substrate mounting stage whose surface has a thermally sprayed coating film formed thereon, and a surface treatment method therefor.
2. Description of the Related Art
Substrate processing apparatuses that carry out plasma processing such as etching processing on wafers as substrates have a housing chamber in which a wafer is housed, and a mounting stage that is disposed in the housing chamber and on which the wafer is mounted. In such substrate processing apparatuses, plasma is produced in the housing chamber, and the wafer is subjected to the etching processing by the plasma.
The mounting stage has in an upper portion thereof an electrostatic chuck comprised of an insulating member having an electrode plate therein, the wafer being mounted on the electrostatic chuck. While the wafer is being subjected to the etching processing, a DC voltage is applied to the electrode plate, the electrostatic chuck attracting the wafer thereto through a Coulomb force or a Johnsen-Rahbek force generated by the DC voltage.
Moreover, a coolant chamber is provided inside the mounting stage. A coolant, for example cooling water or a Galden (registered trademark) fluid at a predetermined temperature is supplied into the coolant chamber from a chiller unit. A processing temperature of the wafer attracted to and held on a surface of the electrostatic chuck is controlled through the temperature of the coolant.
Conventionally, first, a thermally sprayed coating film is formed on the surface of the electrostatic chuck by thermally spraying with a ceramic such as alumina. Next, a grindstone obtained by compacting together abrasive grains and making into a disk shape is brought into contact with the surface of the electrostatic chuck on which the thermally sprayed coating film has been formed. The grindstone is then rotated, and also moved parallel to the surface of the electrostatic chuck on which the thermally sprayed coating film has been formed. As a result, the surface of the electrostatic chuck is ground, i.e. processed.
However, an electrostatic chuck processed using the conventional method has a rough surface when viewed microscopically, and furthermore there are minute undulations on the surface of the electrostatic chuck. A wafer attracted to and held on the electrostatic chuck contacts the surface of the electrostatic chuck, and hence the temperature of the wafer depends on the contact area between the wafer and the surface of the electrostatic chuck. If the surface of the electrostatic chuck is rough, then there is a problem that the contact area between the wafer and the surface of the electrostatic chuck is small, and hence the thermal contact resistance of the contacting portion becomes high, and the efficiency of heat transfer from the electrostatic chuck to the wafer becomes poor.
To address the above described problem, the present inventors proposed an electrostatic chuck processing method in FIGS. 9A to 9H. In this processing method, first, a thermally sprayed coating film 1 is formed on a surface of an electrostatic chuck 42a by thermally spraying with a ceramic such as alumina (FIG. 9A), and a grindstone 2 obtained by compacting together abrasive grains and making into a disk shape is brought into contact with the surface of the electrostatic chuck 42a on which the thermally sprayed coating film 1 has been formed (FIG. 9B). The grindstone 2 is then rotated, and also moved parallel to the surface of the electrostatic chuck 42a on which the thermally sprayed coating film 1 has been formed. The electrostatic chuck 42a is also rotated about an axis of rotation shown by the alternate long and short dash line in FIG. 9C, and as a result, the surface of the electrostatic chuck 42a is ground rough (FIG. 9C). Next, a lapping plate 3 onto a surface of which is sprayed a slurry in which are mixed abrasive grains and a lubricant is brought into contact with the surface of the electrostatic chuck 42a that has been ground rough as shown in FIG. 9D. At this time, a load (shown by the white arrow in FIG. 9E) is applied to the lapping plate 3, and the electrostatic chuck 42a is rotated about an axis of rotation shown by the alternate long and short dash line in FIG. 9E, so that the surface of the electrostatic chuck 42a is ground flat (FIG. 9E). Then, by applying a load (shown by the white arrows in FIG. 9G) to a tape lapping apparatus 4 that has a tape 5 whose surface has abrasive grains 9 coated and fixed thereon and a roller 6 made of an elastic material, the tape 5 is brought into contact with the surface that has been ground flat (FIG. 9F). At this time, the tape 5 wound on the roller 6 is wound in and wound out by the tape lapping apparatus 4, the tape lapping apparatus 4 is moved parallel to the surface of the electrostatic chuck 42a, and the electrostatic chuck 42a is rotated about an axis of rotation shown by the alternate long and short dash line in FIG. 9G (FIG. 9G). As a result, the surface as shown in FIG. 9H can be obtained (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2007-258240).
The electrostatic chuck 42a proposed by the present inventors can increase the contact area between a wafer W and the surface of the electrostatic chuck 42 when the wafer W is attracted to the surface of the electrostatic chuck 42a, and hence improve the efficiency of heat transfer between the wafer W and the surface of the electrostatic chuck 42a (FIG. 10A), but has a problem that when deposit or particles, for example CF type deposit D, arising as reaction product from plasma processing become attached to the surface of the electrostatic chuck 42a, the contact between the wafer W and the surface of the electrostatic chuck 42a is obstructed by the deposit D, and the wafer W cannot be attracted to the surface of the electrostatic chuck 42a (FIG. 10B).
If the contact between the wafer W and the surface of the electrostatic chuck 42a is obstructed by the deposit D, and the wafer W is caused to float above the surface of the electrostatic chuck 42a (FIG. 10B), helium gas as a heat transfer gas supplied into a gap between the wafer W and the surface of the electrostatic chuck 42a leaks from the gap. Upon detecting the leakage of the helium gas, the substrate processing apparatus recognizes poor attraction of the electrostatic chuck 42a and stops operating. To resume operation of the substrate processing apparatus, it is necessary to carry out maintenance such as cleaning the surface of the electrostatic chuck 42 and removing the deposit D, and hence there is a problem that the operating rate of the substrate processing apparatus is markedly decreased. This problem may arise not only in substrate processing apparatuses that subject oxidative objects to etching processing using CF type gas as a processing gas, but also in all the substrate processing apparatuses that use a processing gas from which a large amount of reaction product is produced, and all the substrate processing apparatuses that carry out processing in which a large number of particles and the like become attached to an electrostatic chuck.